ZnCl2 Incorporated into Experimental Adhesives: Selected Physicochemical Properties and Resin-Dentin Bonding Stability

The aim of this study was to evaluate the degree of conversion (DC%), water sorption (WS), solubility (SO), and resin-dentin bonding stability of experimental adhesive systems containing ZnCl2. Different concentrations (wt.%) of ZnCl2 were added to a model etch-and-rinse adhesive system consisting of BISGMA, HEMA, UDMA, GDMA, water, and ethanol: Zn0 (0%-control group); Zn2 (2%); Zn3.5 (3.5%); and Zn5 (5%). Adper Single Bond 2 (SB) was used as commercial reference. The samples were light cured for 20s using a quartz-tungsten-halogen unit (650 mW/cm2). DC% ( n=5 ) was measured using FT-IR spectroscopy, and WS and SO ( n=5 ) were calculated based on ISO4049. Microtensile bond strength (μTBS) and nanoleakage (NL) were measured after 24 h and 12 months of water storage ( n=10 ). Data were analyzed using ANOVA and Tukey’s HSD test (5%). Zn5 presented the lowest DC% and the highest WS and SO ( p<0.05 ). Zn0 and Zn2 presented statistically similar DC%, WS, SO, and immediate μTBS. All adhesives containing ZnCl2 maintained a μTBS stability after 12 months, but only Zn2 and Zn3.5 did not suffer an increase in NL. SB presented the highest immediate μTBS but the greatest reduction after 12 months ( p<0.05 ). The addition of 2 wt.% of ZnCl2 in adhesive formulations seems to be a promising way to improve the resin-dentin bonding stability. Higher concentrations than 2 wt.% could impair some physicochemical properties.